Ive said this before but i really dont like the idea of NPH as Riddler. The guy doesn't have the range to be a more serious take on the Riddler than what we've seen in the past.

There's 2 ways to do it. The Jesse Eisenberg way. Meaning, the nerdy, thin, socially awkward Nygma. Whether it be the traditional way or some kind of hacker to fit with the modern times. Someone like Paul Dano or Michael Emerson if you want older would work very well. Casey Affleck could have worked if his bro wasn't playing Batman.